A few chemistry questions (haven't really covered this yet!)

1)
Standard enthalpy of combustion/kJmol^01
S(rhombic) -296.9
S(monoclinic) -297.2

a)i Calculate the standard enthalpy change for the conversion of rhombic sulphur to monoclinic sulphur.

a)ii From your answer to a)i state, with reason, which allotrope of sulphur is the more stable under standard conditions.

2) Write a balanced chemical equation to represent the standard enthalpy of formation for magnesium carbonate.

3) State, giving a reason, how you would expect the enthalpy of hydrogenation of but-1-ene to change if platinum were to be used as a catalyst instead of nickel.

Reply 1

charco

Study Forum Helper

And in reverse order...

3. No change - the catalyst only affects the mechanism not the energy of reactants or products

2. Mg(s) + C(s) + 3/2O2(g) --> MgCO3(s)

1. S(mono) + O2 --> SO2 energy = -297.2
S(rhom) + O2 --> SO2 energy = -296.9

subtract 2nd from 1st
S(mono) - S(rhom) --> nothing energy = -0.3
rearrange
S(mono) --> S(rhom) energy = -0.3

therefore rhombic is the most stable as its formation is exothermic from monoclinic